Centrifugal compressor and method of controlling the same



Dec. 24, 1957 A. M. G. MOODY 2,317,475

CENTRIFUGAL COMPRESSOR AND METHOD OF CONTROLLING THE SAME Filed Jan. 22,1954 5 Sheets-Sheet 1 INVENTOR. ARTHUR M. G. MOODY 3 7L 4mm,

A TTORN E (S Dec. 24, 1957 A. M. G. MOODY 2,817,475

- CENTRIFUGAL COMPRESSOR AND METHOD OF CONTROLLING THE SAME Filed Jan.22, 1954 3 SheetsSheet 2 INVENTOR. ARTHUR M. G. MOODY Mm, um

ATTORNEYS A. M. G. MOODY CENTRIFUGAL COMPRESSOR AND METHOD OFCONTROLLING THE SAME Dec. 24, 1957 3 Sheets-Sheet 3 Filed Jan. 22, 1954ATTORNEYS United States Patent 2,81 7,475 Patented Dec. .24, 1957CENTRIFUGAL COMPRESSOR AND METHOD OF CONTROLLING THE SAME Arthur M. G.Moody, La Crosse, Wis., assignor to The Trane Company, La Crosse, Wis.,a corporation of Wisconsin Application January 22, 1954, Serial No.405,525 2 Claims. (Cl. 230-114) This invention relates to centrifugalcompressors and particularly to compressors which have means forcontrolling the capacity over a wide range. Prior to this inventioninlet guide vanes have been used to control the capacity of centrifugalcompressors. However, it has been impossible to reduce the capacity of amulti-stage compressor beyond a certain minimum at which surge occurs.

It is an object of this invention to provide a control for theadjustable inlet vane of a multi-stage centrifugal compressor which willreduce the point at which surge occurs and thus increase the operatingrange of the compressor.

It is a further object of this invention to provide control mechanismhaving a single motor to adjust the guide vanes of each stage todifferent angular positions with respect to the fiow.

Other objects and advantages of this invention will appear as thespecification proceeds to describe the invention with reference to theaccompanying drawings, in which:

Figure l is a plan view of the compressor including the controlmechanism.

Figure 2 is the end view taken from the right hand side of Figure 1.

Figure 3 is an end view taken from the left hand side of Figure 1.

Figure 4 is a sectional view taken on line 4-4 of Figure 5.

Figure 5 is a sectional view taken on line 5-5 of Figure 2.

Figure 6 is a view of the control mechanism showing the relativepositions of the controls for each stage.

Figure 7 is a chart showing the relative angular positions of the guidevanes for each of the two stages.

Figure 8 is a view of the compressor including the pipe between stages.

The compressor illustrated has an electric motor 10. Other suitableprime movers might be used instead of the electric motor 10. At one endof the electric motor 10 is the first stage 12 of the compressor. To theother end of the electric motor 10 is secured the second stage 14 of thecompressor. The motor 10 has a shaft 16 which has a shaft extension ateach end to which are secured the impellers for the stages 12 and 14.Figure 5 shows impeller 18 mounted in the housing of the first stage 12and secured to the end of shaft 16 by a nut 20. Another impeller notshown is mounted on the other end of the shaft 16 in the housing of thesecond stage 14.

An inlet housing 22 conducts gas to the first stage 12 of thecompressor, and a similar inlet housing 23 conducts gas to the secondstage 14 of the compressor. A cross-over pipe 21 conducts gas from thedischarge opening 26 of the first stage to the inlet 23 of the secondstage. The compressed gas is discharged from the compressor throughopening to which a discharge pipe, not shown, is secured.

An adjustable inlet vane mechanism is mounted in inlet housing 22. Asimilar adjustable inlet vane mechanism is mounted in housing 23 of thesecond stage. It will suffice, therefore, to describe in detail only theinlet vane mechanism of the first stage since that of the second stageis similar. A plurality of inlet vanes 24 are secured to shafts 28 whichare rotatably mounted in a vane housing 27. An arm 30 is fixedly securedto each shaft 28, and links 32 are pivotally connected to arms 30 and toa control ring 34 which is rotatably mounted on vane housing 27 by meansof ball bearings 36.

A lever 38 is fixedly mounted in a bracket 40 which is pivoted tohousing 22 at 42. The inner end of lever 38 is pivotally secured to alug 44 on the ring 34. A flexible metal bellows 46 surrounds lever 38and is sealed at one end to housing 22 and at the other end to bracket40. The bellows 46 seals the opening in inlet housing 22 through whichlever 38 extends but it permits movement of the lever 38 all as shown inFigure 3. Guide vanes 48 are pivotally mounted in the inlet 23 of thesecond stage in a manner similar to the mounting for the vanes 24 in theinlet 22 of the first stage. A lever 50 extends from housing 23 and isconnected to vanes 48 by a mechanism similar to that described withreference to the vane control for the first stage.

A fluid motor 52 is pivotally secured at 54 to motor 10. Fluid motor 52is of a well known type having a fluid pressure actuated piston ordiaphragm to which is secured the rod 56. Fluid motor 52 is connected toa source of pressure not shown and the pressure is modulated accordingto the capacity desired from the compressor. A control shaft 58 isrotatably mounted in bearings 60 and 62 which are secured to stages 12and 14 respectively. An arm 74 is fixedly secured to shaft 58 and theouter end of arm 74 is pivotally secured to rod 56. It is thus evidentthat motor 52 acting through rod 56 and arm 74 controls the rotativeposition of shaft 58. A crank 64 is secured to shaft 58 at one end and acrank 66 is secured to shaft 58 at its other end. A connecting rod 70 ispivotally secured at one end to crank 64 and at the other end to lever38. A connecting rod 72 is pivotally secured at one end to crank 66 andat its other end to lever 50.

I have found that as the capacity of the compressor is reducedconsiderably from full load capacity, the second stage receives areduced volume of gas from the first stage and the compressor will tendto surge unless the spin vanes at the inlet of the second stage areinclined at a greater angle to flow than are the vanes of the firststage. The desired relative angular positions of the vanes are showngraphically in Figure 7. In order to obtain the relative angular vanepositions of Figure 7, the cranks 64 and 66 are angularly spaced on theshaft 58. Figure 6 shows the control mechanism in a position in whichthe vanes of both stages are fully closed. In order to move the vanesfrom fully closed to fully open position crank 66 will move through theangle B and crank 64 will move through the angle A. It can be seen byreference to Figure 6, which shows the mechanism in a position forclosed vanes, that counterclockwise movement of arm '74- will causerelatively rapid initial angular movement of the vanes 24, and theangular position of crank 66 will cause relatively slow initial angularmovement of vanes 48. The correct angular position of cranks 64 and 66can be determined by experiment.

Although the invention has been shown .in connection with a two stagecompressor, it is also applicable to a compressor having more than twostages. For instance, a three stage compressor would have a control forsubstantially reduced output in which the control would hold the spinvanes of each stage at a greater angle with respect to flow than that ofthe vanes of the next preceding stage.

While one embodiment of the invention has been described for the purposeof illustration, it should be understood that the invention is notlimited to the exact apparatus and arrangement of apparatus illustrated,as modifications thereof may be suggested by those skilled in the artwithout departure from the essence of the invention, and I desire to belimited only by the claims.

I claim:

1. A centrifugal compressor comprising a first and a second stage eachhaving an impeller, an inlet, and an outlet, means for conducting gasfrom the outlet of the first stage to the inlet of the second stage,spin vanes pivotally adjustably mounted in the inlet of said first stageabout axes radial to the axis of rotation of the impeller of said firststage, spin vanes pivotally adjustably mounted in the inlet of saidsecond stage about axes radial to the axis of rotation of the impellerof said second stage, a motor, a first crank driven by said motor, afirst connecting rod driven by said first crank and connected to thespin vanes of the first stage for angularly adjusting the same, a secondcrank driven by said motor, a second connecting rod driven by saidsecond crank and connected to the spin vanes of the second stage forangularly adjusting the same, said second crank and said secondconnecting rod making a greater angle than said first crank and saidfirst connecting rod when the spin vanes of both stages are in closedposition whereby when the spin vanes angularly are adjusted between openand closed position, the spin vanes of the first stage are inclined at alesser angle with respect to flow than the spin vanes of the secondstage.

2. A centrifugal compressor comprising a first and a second stage eachhaving an impeller, a circular inlet and outlet, means for conductinggas from the outlet of the first stage to the inlet of the second stage,sector shaped vanes pivotally mounted in the inlet of said first stagein cooperative relationship about axes in planes radial to the axis ofthe inlet of said first stage, sector shaped vanes pivotally mounted inthe inlet of said second stage in cooperative relationship about axes inplanes radial to the axis of the inlet of said second stage, a motor, afirst crank driven by said motor, a first connecting rod driven by saidfirst crank and connected to the sector shaped vanes of the first stagefor angularly adjusting the same, a second crank driven by said motor, asecond connecting rod driven by said second crank and connected to thesector shaped vanes of the second stage for angularly adjusting thesame, said second crank and said second connecting rod making a greaterangle than said first crank and said first connecting rod when thesector shaped vanes are in closed position whereby when the sectorshaped vanes are adjusted between open and closed position, the sectorshaped vanes of the first stage are inclined at a lesser angle withrespect to flow than the sector shaped vanes of the second stage.

References Cited in the file of this patent UNITED STATES PATENTS1,075,300 Moss Oct. 7, 1913 2,142,596 Algarsson Jan. 3, 1939 2,170,974Parkins Aug. 29, 1939 2,360,386 Young Oct. 17, 1944 2,671,604 Hagen Mar.9, 1954

